1. Field of the Invention
The subject invention generally relates to a position tracking system. More specifically, the subject invention relates to a position tracking system that includes an infrared-sensitive device for detecting infrared light, a processor for determining a position of the detected infrared light and for generating tilt and pan signals based on the position, and a tilt and pan mechanism for moving a visible-light video camera in response to the tilt and pan signals from the processor.
2. Description of the Related Art
Position tracking systems are known in the art and function through a number of different mechanisms in order to track a moving object. More specifically, the position tracking systems typically include a camera that detects either visible or infrared light. The camera may function by detecting visible or infrared light reflected from an object, by detecting disturbances in ambient visible or infrared light resulting from movement of the object within a field of view of the camera, or by detecting visible or infrared light emitted from a light-emitting device attached to the object. One such position tracking system is disclosed in United States Patent Publication No. 2005/012291 to Murakami.
The '291 publication discloses a visible light camera and an infrared camera for detecting light depending on the time of day, i.e., whether visible light is available from sunlight or whether only infrared light is available. The cameras generate signals in response to disturbances in detected light in the field of view of the camera, which result from movement of an object such as a person in the field of view. A processor is responsive to the signals generated by the camera. The processor uses an algorithm to determine a position of the object based on the signals from the cameras. The processor generates tilt and pan signals based on the position determined by the processor. The processor communicates the signals to tilt and pan mechanisms attached to the cameras. The tilt and pan mechanisms move the cameras in response to the tilt and pan signals from the processor in order to track the object.
With the tracking system of the '291 publication, other moving objects may be in the field of view of the cameras, thereby skewing the signals generated by the cameras and causing inaccuracies in the tilt and pan signals generated by the processor. Further, if the moving object were to enter an area of direct sunlight or other bright light, the visible light camera may detect a washed image in the area of the direct light, thus causing the tracking system to lose track of the object. The object may move behind other objects within a field of view of the camera, which may obscure the object from view and cause the tracking system to lose track of the object. Different lighting regions may also persist within the field of view of the camera that affect the signals generated by the camera. Each of these factors may affect the performance of the tracking system.
Another position tracking system is disclosed in U.S. Pat. No. 5,023,709 to Kita et al. The '709 patent discloses an infrared camera that generates signals in response to detected infrared light in a field of view of the infrared camera. The detected infrared, light originates from a “marker”, which may be a strip of reflective tape that reflects infrared light that is applied to it or an infrared radiant that radiates infrared rays when infrared light is applied to it. The marker is affixed to a moving object, such as a person. The infrared light may originate from an infrared irradiation apparatus mounted adjacent to the infrared camera. A processor is responsive to the signals generated by the camera. The processor uses an algorithm to determine a position of the detected light based on the signals from the camera. The processor generates tilt and pan signals based on the position determined by the processor. The processor communicates the signals to tilt and pan mechanisms attached to the cameras. The tilt and pan mechanisms move the cameras in response to the tilt and pan signals from the processor.
With the tracking system of the '709 patent, the object having the mark affixed thereto may move behind other objects within a field of view of the camera, thus obscuring the mark from view and causing the tracking system to lose track of the mark. Further, the mark may be obscured beneath clothing, thereby causing the tracking system to lose track of the mark. Further obstruction may occur simply by the object rotating relative to the infrared camera, thereby obscuring the mark from view behind the rotating object. The infrared light may also reflect off of shiny surfaces, thereby skewing the signals generated by the infrared camera and causing the tracking system to lose track of the object.
U.S. Pat. No. 6,801,637 to Voronka et al. discloses another tracking system. The tracking system of the '637 patent employs a series of active markers that emit infrared light and that are placed at different points on a person's body. The sensors are pulsed such that only one sensor is emitting infrared light at any point in time. A position sensor includes three cameras that separately detect a position of each sensor, and relative movements of different body parts are tracked by compiling the data relative to each of the sensors. However, the cameras have a fixed field of view and cannot follow the sensors if the sensors move from the fixed field of view of the cameras. Further, the sensors are each attached to a control box through a wire. With the sensors being positioned at different points on the body, installation of the sensors is cumbersome and time consuming. With the sensors placed all over the body, the sensors are discrete and distracting. As such, the tracking system of the '637 patent is not suitable for all manner of position tracking applications.
U.S. Pat. No. 5,179,421 to Parker et al. and assigned to ParkerVision, Inc. also discloses another tracking system. Details of the tracking system disclosed in the '421 patent are further clarified in the cited product information for the “CameraMan” products from ParkerVision, Inc. The tracking system includes an infrared transmitter that transmits infrared light to an infrared receiver that is placed behind a rotating set of signal blocking blinders whose position at any time defines a view angle with a known position. The infrared receiver scans a field of view and detects a peak signal strength from the infrared transmitter. A processor then determines tilt and pan angles and positions a video camera based on the detected position of the peak signal strength. However, as stated in the “CameraMan: 3 ccd Presenter Camera System” Installation and Operations Manual, the infrared transmitter requires a direct line-of-sight link with the camera, i.e., the infrared receiver. Further, no hair or clothing can cover the sensors. Such features make the tracking system of the '421 patent cumbersome and may distract a person wearing the infrared transmitter. By scanning for a peak signal strength, the sensor of the '421 patent is susceptible to ambient infrared light reflecting off of shiny objects, as well as other sources of infrared light. Finally, as shown in the Installation and Operations Manuals, although the infrared transmitter may include infrared light-emitting elements disposed along a loop, a control box is not part of the loop and must be separately connected to the loop through a cable, thus making the infrared transmitter bulky and distracting.
Due to the deficiencies of the prior art, there remains an opportunity to provide a position tracking system and a method of tracking with the position tracking system that provides a constantly viewable source of infrared light to an infrared camera such that tracking is unimpeded, regardless of whether or not the source of infrared light is covered by clothing, hair, etc. There is also an opportunity to provide a position tracking system that may be set up quickly and that is not distracting to observers of a person being tracked.